Method and apparatus for receiving wireless signals



Sept. 29, 1931. w. M. BRUCE I 1,824,803

METHOD AND APPARATUS FOR RECEIVING WIRELESS SIGNALS Filed April 30,19284 Sheets-Sheet l I [1. J d7 4:

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Sept. 29, 1931. w. M. BRUCE METHOD AND APPARATUS FOR RECEIVING. WIRELESSSIGNALS Filed April 30, 1928 Sheets-Sheet 2 Sept. 29, 1931. w. M BRUCE1,824,803

METHOD AND APPARATUS FOR RECEIVING WIREIJESS SIGNALS Filed April 30,1928 4 Sheets-Sheet 3 Sept. 29, 1-931. w. M. BRUCE 1,824,803

METHOD AND APPARATUS FOR RECEIVING WIRELESS SIGNALS Filed p il 1928 4Sheets-Sheet 4 b m fiat I 4- 7 a 1 Ila-B 1 D L g 1 .+B.nt7'- avwcmtoi35% WWM PatenteclJSept. 29, 1931 I' N E YSTA ES PATE T FF wI 'nIArr-m.nat on, or SPRINGFIELD, OHIO' METHOD AND nrrnnarnsroa RECEIVING WIRELESSSIGNALS Application filed April 30,

- My invention relates to methods and apparatus for receiving wirelesssignals or high frequency oscillations. a.

- The object of my invention is to provide methods and meansforeliminating from the circuits of a wireless receiving apparatustheso-called static or disturbing impulses or ose cillations so that-thedesired signals can be received free from such disturbances;

to In carrying out my invention I make' use of the-well knownprinciple'that if two currents of opposite-phase or polarity, but havingthe same frequency and characteristics are impressed upon the samecircuit they will cancel or neutralizeeach-other and of the furtherprinciple that by the aid of properly constructed apparatus as isusually included under the-term filter a single definite frequency canbe stopped and other frequen= cies-will pass through the circuit. a

/ In its simplest form I employ in an ordi nary wireless receivingapparatus a local circuit including a filter preferably having variabletuning and I connect this local circuit to theregular'receivingcircuitinsuch a way that the local receiving circuit has impressed uponit all of the incoming oscillations and impulsesin the usualmanner. Bythe aid of the filter or equivalent devices I prevent the. passage.through this auxiliary circuit of the frequency which it is desired toreceive in the receiving set. The other frequencies are allowed to'passthrough toithe local circuit and are then impressed upon the circuit ofthe regular receiving appartaus in such a manner that all impulses oroscillations having-like frequencies or characteristics arecancelled'.Thus the.tuned in incoming frequency is the only one which will passthrough the regular receiving circuit free from the static or otherdisturbing influences which have been concelled by like frequencies ordisturbances of opposite phase impressed thereon.

In the accompanying drawings which are diagrams of various circuits andmodifications embodying my invention; r I

Fig. l'shows a well known type of superheterodyne circuit to which myinvention has u been applied.

Fig. 2 shows my invention applied to a 1928.' Serial N0: 273,869.

simple receiving circuit of well known form having asingle amplifyingtube.

Fig. 8is a similar circuit in which a special form of tube with multiplegrids is shown. 4 is a view of a similar circuit with slightmodification in the wiring connections; Fig. 5 is a diagram of a wellknown circuit having two radio amplifying tubes and a local cancellingcircuit, which also has therein an amplifying tube.

Fig. 6 is a similar view with slight modifications. Iv Fig.3 7- is adiagram showing the application of my' invention to a receiving circuitsuch as is used in the reception of wireless telegraphy or undampedoscillations with a local heterodyne.

" Figs-8 and 9 are views showing modifications and including amplifyingtubes in the auxiliary circuit.

" Fig.10-is a'detail view showing a special form of filter.

. "Figs. 11 and 12 are modifications in which 'an amplifierand'oscillator are used in the auxiliary or cancelling circuit. 7

Referring to Fig. 2 in which a circuit of simple form isshown 1represents an ordinary radio amplifying tube. Theaerial A'is connectedby transformer T, with the usual-variable condensento the grid of thetube and the plate circuit of the tube isconnected through transformer Tto the next succeedingtube or receiving device. These parts having theusual A; B and C battery connections as shown.

Extending around thetube 1 from the aerial connection to the platecircuit and the primary coil of the transformer T- I provide anauxiliary or cancelling circuit 9 including a filter '13 which ispreferably made with variable parts by which it may be made resonant toany desired frequency. There is also preferably included in this circuita variable condenser 15 connected to the filter by wire 12 to preventfiow of plate battery 5 throughthe filter and to regulate the amplitudeof the impulse. I

In the'operation of this circuit the regular receivingdevice will betuned to a certain definite frequency which is adapted tobe received bythe receiving set. There will be usually included with this frequencycertain other disturbing frequencies such as static or othercharacteristic currents which cannot ordinarily be tuned out by theusual tuning devices and they will pass throughithe amplifying tube andthrough the transformer T at the. same time there will beset up in theauxiliary or cancelling circuit 8, 12, 9, frequencies having likecharacteristics as those in the main circuit except that by reason ofthe transposition in the transformer they willbe in opposite phase orpolarity. By bringing the filter 13 into resonance with the mainfrequency or signal carrying wave intended to. be received that,particular frequency will be prevented by the filter from passingthroughthe local. or auxiliary circuit. There will therefore be impressed uponthe. receiving circuit in. opposite phase or polarity all frequencies,oscillations etc.

received by the set, other than the. desired frequencies. (which will bestopped by the auxiliary or filter circuit). and these being impressedupon the regular receiving circuit will cancel or eliminate all of thedisturbing factors leaving only the main signal carrying'wave orfrequency to pass'through the receiving circuit and to-the finaltranslating device. Y

Figs. 3; and 4 arediagrams similar to Fig. 2 with slight modificationsin the-wiring and connections. In each case the filter-13 isin theauxiliary or.- cancelling circuit 9, 12 and 8. There is however avariable resistance R connected in the circuit and, a. fixed condenser15, these being for the purpose. of varying the amplitude of the.impulses passing through, the auxiliary circuit.

In Fig. 3 whichv shows a tube having multiple-gnids the auxiliarycircuit is connected tothe. auxiliary grid of the tube instead of theregular grid.

Fig. 1- on the same sheet showstheinven: tion applied. to a usual formof superhetero; dyne. receiving circuit. In this figure A shows thesource of theincoming high frequency oscillations and B represents thesource of. local oscillations. 1, 2 and3 represent the tubes of which 1is the first detector and 2and 3 theintermediate stages of radiofrequency amplification. The wires 6- and 7. lead to the second detectorin. the usual manner.

Two-auxiliary circuits with two filters are shown here, one around thedetector 1 and the other aroundthe radio amplifying tube-3, theconnections and arrangements are substantia-llythe same as shownin Fig.4.

A s'uperheterodyne receiving circuit lends itself readily to theapplication of my. invention from the fact that theradio frequencystages ofamplification have at all times a single and fixed frequencytoamplify and the filter or filters maybe designed and-tuned in apermanent manner, no adjustment of the filter being necessary whendifferent incoming high frequency oscillations or wave lengths are beingselected.

Figs. hand 6 show further modifications and also show the inventionapplied to other forms ofreceiving circuits. In these figures theauxiliary circuit including the filter also has an amplifying tube 10 sothat the impulses and oscillations which pass through the auxiliarycircuit may be amplified and-regulated so. that the strength ofthecancelling impulses and oscillations will equal in amplitude likeimpulsesv and oscillations in the circuit of the receiving set.

In Fig. 5' the transformer]? is. showrr with a. double wound and.differentially connected primary 5 to which the auxiliary circuit isconnected and. by means of which the opposite phase or polarity for theimpulses: passing through the auxiliary circuit and filter are secured.

Fig. 6; shows substantially. the: same; arrangement in which the usualby pass cons densers G and C1 are shown in connection with the audio.transformer which has thediffentially wound primary 5.

Figs/T. shows a type of wirelessreceivin-g c rcuit especially adaptedfor the. reception of wireless telegraphy or; undampedoscillations. Inthis. figure numerals. 1', and2 are radio. frequency amplifying tubesshown with transformer coupling. 3 is a detector and wires 6 and 7 leadto the next stage of audio frequency amplification. B shows a localsource of oscillations which if desired may include the-plate circuit ofthe detector tube to. operate: as a selfheterodyne. The. local circuitisshown connected by'wire 9to: the second winding-of the radio transformerT and; includes the filter 1-3 with variable. re? sistance R andcondenser 14 being so con.- nected that the-relativephase angleandamplitude of disturbingimpulses and. oscill'ae tions will cancel andeliminate like'and-cornespending impulses and oscillations that arepnesentin the grid. circuit of'tube 11..

Fig: 8 is. a. somewhat modified: circuitin which a nadiofrequencyamplifying tube 10 is used in the auxiliary circuit whose-plate circuitis connected to-the positive 13 battery by resistance lfiand wire 18.The filter 13 whenproperly adjusted willstop the desired tuned in or'select'edi wave length in. the receiving' circuit and at the same timeallow the disturbing influences and oscillations t'o beimpresseduponthe-grid of the tube 10 by wire 9. These will in turn beamplifiedainthe plate circuit of tube 10in such'mannerthat theirrelative phase an le andamplitudewill cancel and eliminate lilie. andcorresponding impulses and oscillations in the grid circuit of tube 1'.I

Fig. 9 shows a somewhat similiarar-rangement with. an: amplifying radiofrequency tube 10 in the local circuit with the filter 13.

Fig. 10 is a detail arrangement of a filtering device which consists oftwo parallel resonance circuits in series comprising the inductances13and 14 respectively connected in parallel with condensers 5 and 6. Thewire 8 connects the two units in series. variable condenser 3 ispreferably used to control the amplitude of the oscillations that arepermitted to pass through the filter. If desired the condensers 5 and 6vmay be on the single shaft for operating the tuning condensers inunison.

Fig. 11 shows another common form of receiving circuit to which theinvention is applied. The auxiliary cancelling or filter circuitincludes aradio frequency amplifying tube 10 and also a local oscillator11, the oscillations of which will be modulated by the oscillations ordisturbing frequencies which are not stopped by the filter. Thesemodulated oscillations are detected and amplified by the detector 10 andthe circuit is connected to the differential winding 5 of thetransformer T through the differential winding so that the frequenciesof the oscillations will be of the opposite phase or polarity as in theother figures described.

In the construction shown in Fig. 11 in which a local oscillator 11 isused in the cancelling or filtering circuit it is possible under certainconditions to dispense with the filter as the oscillator can be arrangedto accomplish the results desired without the necessity of the filter.This would be particularly true in the broadcasting band now in use offrom say 200 to 500 meters. The oscillator would be adjusted to acomparatively low radio fre uency, or say a frequency of 20,000 cyclesan if the incoming or selected frequencies were of the nature of 600,000cycles or an equivalent wave length of 500 meters,

this would have a negligible efiect in modulating the frequencies of theoscillator as any one cycle of the 600,000 would have approximately .03of the 20,000 cycle frequency that i it could possibly modulate.

The disturbing frequencies of audio frequency will modulate theoscillations of. the

oscillator and can be combined with the receiving circuit in the mannerbefore described to eliminate these modulated fre-' quencies from thecircuit of the receiving set.

This is particularly true also of such disturb-' ances as come from thebeat note or heterodyning of two broadcasting stations of differentfrequencies. With this arrangement the local oscillations modulated bythe dis turbing oscillations would be impressed upon the receivingcircuit and cancel corresponding frequencies and oscillations in themain or receiving circuit.

Fig. 12 shows another conventional form of circuit with two amplifyingtubes 10 and 11 in the auxiliary or filter circuit. These tubes"represent a-resistance coupled amplifier with tuberll 'functioning as adetector. 15 represents aapotentiometer which is connected to a Cbattery 16 in the usual manner. The "operation so far as the filter andeliminatingfunction of the circuit are concerned are similar to thosealready described. It will be seen from the above description that theinventionherein described for eliminating'all of the oscillations ordisturbing frequencies except the one to be received which is stopped bythe filtercircuit is readily adapted'to various forms of circuits inapparatus now inuse, I

It will be understood that the various circuit drawings are merelytypical and are not intended to show all the various refinements usedin. present-.wirelesssets, which may be readily applied withoutin anyway-interfering with the operation of thefilter or cancel-.

ling circuit which will permit all undesirable frequencies to passthrough the said 131- tering circuit with an opposite phase or polarityfrom those in the main receiving, circuitand cancel the same whilethemain or desiredfrequency to be received is not permitted to. passthrough the filtering circuit and consequently will be the only onewhich will pass through the main channel 'ofthe receiving set andtothetranslating device and with the elimination of all disturbingfrequencies.

The term lfilter as usedin these specifica-' tions and claims'is meantto describe any circuit such as.parallel resonance, or any combinationof inductance, capacity, reactance, or resistance that can be adj usteo,or connected so as to oppose, and prevent the passage of a singlefrequency only, and at the same moment offer a minimum, or zeroresistance or reactance to, and permit the passage of currents of allother frequencies. The circuit of the filter shown in thevario-us'drawings isconventional, and any one of many Well knowncombinations may. be used.

.Having thus described my invention, I claim:

1. In a wireless receiving set, a filter circuit having means to rejecta given frequency and permit otherv frequencies to pass, said filtercircuit being connected at one end to the plate circuit of a vacuum tubein the regular receiving circuit and at the other end to the gridcircuit of said tube, means for changing the phase of the. frequenciesor oscillations passing through the filter circuit and means in thefilter circuit for bringing the filter into resonance with any desiredfrequency which will thereupon be stopped by said filter and impressingthe other frequencies in opposite phase upon the regular receivingcircuit whereby undesirable frequencies wil be cancelled and eliminated.

2. In a wireless receiving circuit having an amplifying tube, anauxiliary circuit in a shunt around said tube including a filter with,

means to bring the same into resonance With any desired frequency, theconnections to said auxiliary circuit being such that frequenciesimpressed thereon Will be of opposite phase from those in the vacuumtube whereby undesirable oscillations or disturbing frequencies Will becancelled. r Y

,3. In a Wireless receiving circuit having a vacuum tube amplifier, anauxiliary filter circuit connected from the plate to the grid side ofsaid tube With means for stopping the passage therethrough of any givenfrequency With the free passage for other frequencies of opposite phaseto those passing through the amplifying tube whereby disturbinginfluences Will be eliminated or cancelled by impressing upon themsimilar frequencies of like characteristics but of opposite phase.

4:. In a wireless receiving set a thermionic tube, an auxiliary circuitfrom the plate to the grid of said tube having a variable filter Whichmay be brought into resonance vvith and prevent the flow of a givenfrequency While all other frequencies pass uninterruptedly therethrough,means for bringing the frequencies passing through the filter circuitinto opposite phase from those passing through the tube. and amplifyingdevices in'said auxiliary filter'circuit.

5. In a system for receiving Wireless s1gnals having a termionic tube,an auxlhary circuit from the plate to the grid of said tube withco-nnecti'onssuch that the frequencies passing through said tube shallbe impressed upon the auxiliary circiut in an opposite phase, a localoscillator in said auxiliary circuit of a comparatively loW radiofrequency which will be modulated by the disturbing impulses Within therange of audition and impress these modulations upon the receivingcircuit so as to cancel corresponding or like oscillations or impulsesin the main circuit.

(5. In a Wireless receiving circuit havinga vacuum tube, an auxiliaryfilter circuit connected from the plate to the grid side of said tube,and a transformer With its primary connectedto the plate of said tubeWith its secondary Winding included in the auxiliary filter circuit tochange the phase of the oscillations passing through said filter circuitto cancel like oscillations in the main receiving circuit.

In testimony whereof, I have hereunto set.

my hand this 18th day ofAp-ril, 1928.

WILLIAM M. BRUCE.

